Metal alloys for the reflective or the semi-reflective layer of an optical storage medium

ABSTRACT

A silver-based alloy thin film is provided for the highly reflective or semi-reflective layer of optical discs. Alloy additions to silver include gold, rhodium, ruthenium, osmium, platinum, palladium, copper, silicon, cadmium, tin, lithium, nickel, cobalt, indium, chromium, antimony, gallium, boron, molybdenum, zirconium, beryllium, titanium, magnesium, and zinc. These alloys have moderate to high reflective and reasonable corrosion resistance in the ambient environment.

PRIORITY CLAIM

This patent application is a continuation of U.S. application Ser. No.10/457,935 filed on Jun. 10, 2003, which is a continuation-in-part ofapplication Ser. No. 10/342,649 filed Jan. 15, 2003, now U.S. Pat. No.6,790,503 issued on Sep. 14, 2004, which is a continuation-in-part ofapplication Ser. No. 10/090,855 filed Mar. 4, 2002, now U.S. Pat. No.6,764,735 issued on Jul. 20, 2004, which is a continuation-in-part ofapplication Ser. No. 09/661,062 filed Sep. 13, 2000, now U.S. Pat. No.6,451,402 B1, issued Sep. 17, 2002, which is a continuation-in-part ofapplication Ser. No. 09/557,135, filed Apr. 25, 2000, (abandoned), whichis a continuation-in-part of application Ser. No. 09/438,864 filed Nov.12, 1999, now U.S. Pat. No. 6,280,811, issued on Aug. 28, 2001, which isa continuation-in-part of application Ser. No. 09/102,163, filed on Jun.22, 1998, now U.S. Pat. No. 6,007,889, issued on Oct. 28, 1998, thisapplication is also a continuation in part of application Ser. No.10/409,037 filed on Apr. 8, 2003, (abandoned), which is a continuationof application Ser. No. 09/834,775 filed on Apr. 13, 2001, now U.S. Pat.No. 6,544,616 B2, issued on Apr. 8, 2003, which claims the benefit ofProvisional Patent Application No. 60/219,843 filed on Jul. 21, 2000.

FIELD OF THE INVENTION

This invention relates to reflective layers or semi-reflective layersused in optical storage media that are made of silver-based alloys.

BACKGROUND OF THE INVENTION

Four layers are generally present in the construction of a conventional,prerecorded, optical disc such as compact audio disc. A first layer isusually made from optical grade, polycarbonate resin. This layer ismanufactured by well-known techniques that usually begin by injection orcompression molding the resin into a disc. The surface of the disc ismolded or stamped with extremely small and precisely located pits andlands. These pits and lands have a predetermined size and, as explainedbelow, are ultimately the vehicles for storing information on the disc.

After stamping, an optically reflective layer is placed over theinformation pits and lands. The reflective layer is usually made ofaluminum or an aluminum alloy and is typically between about 40 to about100 nanometers (nm) thick. The reflective layer is usually deposited byone of many well-known vapor deposition techniques such as sputtering orthermal evaporation. Kirk-Othmer, Encyclopedia of Chemical Technology,3rd ed. Vol. 10, pp. 247 to 283, offers a detailed explanation of theseand other deposition techniques such as glow discharge, ion plating, andchemical vapor deposition, and this specification hereby incorporatesthat disclosure by reference.

Next, a solvent-based or an UV (ultraviolet) curing-type resin isapplied over the reflective layer, which is usually followed by a label.The third layer protects the reflective layer from handling and theambient environment. And the label identifies the particular informationthat is stored on the disc, and sometimes, may include artwork.

The information pits residing between the polycarbonate resin and thereflective layer usually take the form of a continuous spiral. Thespiral typically begins at an inside radius and ends at an outsideradius. The distance between any 2 spirals is called the “track pitch”and is usually about 1.6 microns for compact audio disc. The length ofone pit or land in the direction of the track is from about 0.9 to about3.3 microns. All of these details are commonly known for compact audiodiscs and reside in a series of specifications that were first proposedby Philips NV of Holland and Sony of Japan as standards for theindustry.

The disc is read by pointing a laser beam through the optical gradepolycarbonate substrate and onto the reflective layer with sufficientlysmall resolution to focus on the information pits. The pits have a depthof about 14 of the wavelength of the laser light, and the lightgenerally has a wavelength in the range of about 780 to 820 nanometers.Destructive (dark) or constructive (bright) interference of the laserlight is then produced as the laser travels along the spiral track,focusing on an alternating stream of pits and lands in its path.

This on and off change of light intensity from dark to bright or frombright to dark forms the basis of a digital data stream of 1 and 0's.When there is no light intensity change in a fixed time interval, thedigital signal is “0,” and when there is light intensity change fromeither dark to bright or bright to dark, the digital signal is “1.” Thecontinuous stream of ones and zeros that results is then electronicallydecoded and presented in a format that is meaningful to the user such asmusic or computer programming data.

As a result, it is important to have a highly reflective coating on thedisc to reflect the laser light from the disc and onto a detector inorder to read the presence of an intensity change. In general, thereflective layer is usually aluminum, copper, silver, or gold, all ofwhich have a high optical reflectivity of more than 80 percent from 650nm to 820 nm wavelength. Aluminum and aluminum alloys are commonly usedbecause they have a comparatively lower cost, adequate corrosionresistance, and are easily placed onto the polycarbonate disc.

Occasionally and usually for cosmetic reason, a gold or copper basedalloy is used to offer the consumer a “gold” colored disc. Although goldnaturally offers a rich color and satisfies all the functionalrequirements of a highly reflective layer, it is comparatively much moreexpensive than aluminum. Therefore, a copper-based alloy that containszinc or tin is sometimes used to produce the gold colored layer. Butunfortunately, the exchange is not truly satisfactory because the copperalloy's corrosion resistance, in general, is considered worse thanaluminum, which results in a disc that has a shorter life span than onewith an aluminum reflective layer.

For the convenience of the reader, additional details in the manufactureand operation of an optically readable storage system can be found inU.S. Pat. No. 4,998,239 to Strandjord et al. and U.S. Pat. No. 4,709,363to Dirks et al., the disclosures of which are hereby incorporated byreference.

Another type of disc in the compact disc family that has become popularis the recordable compact disc or “CD-R.” This disc is similar to the CDdescribed earlier, but it has a few changes. The recordable compact discbegins with a continuous spiral groove instead of a continuous spiral ofpits and has a layer of organic dye between the polycarbonate substrateand the reflective layer. The disc is recorded by periodically focusinga laser beam into the grooves as the laser travels along the spiraltrack. The laser heats the dye to a high temperature, which in turnplaces pits in the groove that coincide with an input data stream ofones and zeros by periodically deforming and decomposing the dye.

For the convenience of the reader, additional details regarding theoperation and construction of these recordable discs can be found inU.S. Pat. No. 5,325,351 to Uchiyama et al.; and U.S. Pat. Nos.5,391,462; 5,415,914; and 5,419,939 to Arioka et al.; and U.S. Pat. No.5,620,767 to Harigaya et al., the disclosures of which are herebyincorporated into this specification by reference.

The key component of a CD-R disc is the organic dye, which is made fromsolvent and one or more organic compounds from the cyanine,phthalocyanine or azo family. The disc is normally produced by spincoating the dye onto the disc and sputtering the reflective layer overthe dye after the dye is sufficiently dry. But because the dye maycontain halogen ions or other chemicals that can corrode the reflectivelayer, many commonly used reflective layer materials such as aluminummay not be suitable to give the CD-R disc a reasonable life span. Sobeing, frequently gold must be used to manufacture a recordable CD. Butwhile gold satisfies all the functional requirements of CD-R discs, itis a very expensive solution.

Recently, other types of recordable optical disks have been developed.These optical disks use a phase-change or magneto-optic material as therecording medium. An optical laser is used to change the phase ormagnetic state (microstructural change) of the recording layer bymodulating a beam focused on the recording medium while the medium isrotated to produce microstructural changes in the recording layer.During playback, changes in the intensity of light from the optical beamreflected through the recording medium are sensed by a detector. Thesemodulations in light intensity are due to variations in themicrostructure of the recording medium produced during the recordingprocess. Some phase-change and/or magneto-optic materials may be readilyand repeatedly transformed from a first state to a second state and backagain with substantially no degradation. These materials may be used asthe recording media for a compact disc-rewritable disc, or commonlyknown as CD-RW.

To record and read information, phase change discs utilize the recordinglayer's ability to change from a first dark to a second light phase andback again. Recording on these materials produces a series ofalternating dark and light spots according to digital input dataintroduced as modulations in the recording laser beam. These light anddark spots on the recording medium correspond to 0's and 1's in terms ofdigital data. The digitized data is read using a low laser power focusedalong the track of the disc to play back the recorded information. Thelaser power is low enough such that it does not further change the stateof the recording media but is powerful enough such that the variationsin reflectivity of the recording medium may be easily distinguished by adetector. The recording medium may be erased for re-recording byfocussing a laser of intermediate power on the recording medium. Thisreturns the recording medium layer to its original or erased state. Amore detailed discussion of the recording mechanism of opticallyrecordable media can be found in U.S. Pat. Nos. 5,741,603; 5,498,507;and 5,719,006 assigned to the Sony Corporation, the TDK Corporation, andthe NEC Corporation, all of Tokyo, Japan, respectively, the disclosuresof which are incorporated herein by reference in their entirety.

Still another type of disc in the optical disc family that has becomepopular is a prerecorded optical disc called the digital videodisc or“DVD”. This disc has two halves. Each half is made of polycarbonateresin that has been injection or compression molded with pit informationand then sputter coated with a reflective layer, as described earlier.These two halves are then bonded or glued together with an UV curingresin or a hot melt adhesive to form the whole disc. The disc can thenbe played from both sides as contrasted from the compact disc or CDwhere information is usually obtained only from one side. The size of aDVD is about the same as a CD, but the information density isconsiderably higher. The track pitch is about 0.7 micron and the lengthof the pits and lands is from approximately 0.3 to 1.4 microns.

One variation of the DVD family of discs is the DVD-dual layer disc.This disc also has two information layers; however, both layers areplayed back from one side. In this arrangement, the highly reflectivitylayer is usually the same as that previously described. But the secondlayer is only semi-reflective with a reflectivity in the range ofapproximately 18 to 30 percent at 650 nm wavelength. In addition toreflecting light, this second layer must also pass a substantial amountof light so that the laser beam can reach the highly reflective layerunderneath and then reflect back through the semi-reflective layer tothe signal detector.

In a continued attempt to increase the storage capacity of opticaldiscs, a multi-layer disc can be constructed as indicated in thepublication “SPIE Conference Proceeding Vol. 2890, page 2-9, November,1996” where a tri-layer or a quadri-layer optical disc was revealed. Allthe data layers were played back from one side of the disc using laserlight at 650 nm wavelength. A double-sided tri-layered read-only-discthat included a total of six layers can have a storage capacity of about26 gigabytes of information.

More recently, a blue light emitting laser diode with wavelength of 400nm has been made commercially available. The new laser will enable muchdenser digital videodisc data storage. While current DVD using 650 nmred laser can store 4.7 GB per side, the new blue laser will enable 12GB per side, enough storage space for about 6 hours ofstandard-resolution video and sound. With a multi-layer disc, there isenough capacity for a featured movie in the high-definition digitalvideo format. Silver alloys of the present invention can be used for anyone layer of the multi-layer optical disc.

Currently, there is an interest in adapting CD-RW techniques to the DVDfield to produce a rewritable DVD (DVD-RW). Some difficulties in theproduction of a DVD-RW have arisen due to the higher information densityrequirements of the DVD format. For example, the reflectivity of thereflective layer must be increased relative that of the standard DVDreflective layer to accommodate the reading, writing, and erasingrequirements of the DVD-RW format. Also, the thermal conductivity of thereflective layer must also be increased to adequately dissipate the heatgenerated by both the higher laser power requirements to write and eraseinformation and the microstructural changes occurring during theinformation transfer process. The potential choice of the reflectivelayer is currently pure gold, pure silver and aluminum alloys. Goldseems to have sufficient reflectivity, thermal conductivity, andcorrosion resistance properties to work in a DVD-RW disk. Additionally,gold is relatively easy to sputter into a coating of uniform thickness.But once again, gold is also comparatively more expensive than othermetals, making the DVD-RW format prohibitively expensive. Pure silverhas higher reflectivity and thermal conductivity than gold, but itscorrosion resistance is relatively poor as compared to gold. Aluminumalloy's reflectivity and thermal conductivity is considerably lower thaneither gold or silver, and therefore is not necessarily a good choicefor the reflective layer in DVD−RW or DVD+RW.

For the convenience of the reader, additional details regarding themanufacture and construction of DVD discs can be found in U.S. Pat. No.5,640,382 to Florczak et al. the disclosure of which is herebyincorporated by reference.

Therefore, what is needed are some new alloys that have the advantagesof gold when used as a reflective layer or as a semi-reflective layer inan optical storage medium, but are not as expensive as gold. These newalloys also have better corrosion resistance than pure silver. Thecurrent invention addresses that need.

SUMMARY OF THE INVENTION

It is an objective of this invention to provide new metallic alloys forthin film reflective layers that has high reflectivity and similarsputtering characteristics as gold, and is corrosion resistant yetinexpensive. When a layer of this invention is made thin enough, it canbe semi-reflective and transmissive to laser light and used inapplications such as a DVD-dual layer.

It is another objective of this invention to provide a lower costalternative to the gold reflective layer in a recordable compact discand still satisfy other functional requirements of the disc such as,high reflectivity and corrosion resistance.

It is a further objective of this invention to provide a silver-basedalloy with chemical, thermal, and optical properties that satisfy thefunctional requirements of the reflective layer in a DVD−RW or DVD+RWdisc, and other current or future generations of optical discs in whichreflectivity, corrosion resistance, and ease of application are allimportant requirements for a low cost and high performance product.

In one aspect, this invention is an optical storage medium, comprising:a first layer having a pattern of features in at least one majorsurface; and a first coating adjacent the first layer, the first coatingincludes a first metal alloy; wherein the first metal alloy comprises:silver; and at least one other element, selected from the groupconsisting of copper, silicon, cadmium, tin, lithium, nickel, cobalt,indium, chromium, antimony, gallium, boron, molybdenum, zirconium,beryllium, titanium and magnesium, wherein said other elements arepresent from 0.01 a/o percent to 10.0 a/o percent of the amount ofsilver present. In another aspect of the invention, the aforementionedelements alloyed with silver are present in the amount of 0.1 a/opercent to 5.0 a/o percent. The first coating of the optical storagemedium may directly contact the first metal layer of the medium.

In another aspect of the invention, the medium may further comprise asecond layer having a pattern of features in at least one major surfaceand a second coating adjacent to the second layer. The second layer mayinclude a dielectric material. Additionally, the medium may include athird layer having a pattern of features in at least one major surface,the third layer including an optically recordable material and a forthlayer having a pattern of features in at least one major surface, theforth layer may include a dielectric material.

In another aspect of the invention, the optically recordable material isa phase-changeable material. The optically recordable material maycomprise a phase changeable materials selected from the group consistingof Ge—Sb—Te, As—In—Sb—Te, Cr—Ge—Sb—Te, As—Te—Ge, Te—Ge—Sn, Te—Ge—Sn—O,Te—Se, Sn—Te—Se, Te—Ge—Sn—Au, Ge—Sb—Te, Sb—Te—Se, In—Se—Tl, In Sb,In—Sb—Se, In—Se—Tl—Co, Bi—Ge, Bi—Ge—Sb, Bi—Ge—Te, and Si—Te—Sn. Theoptically recordable material may be a magneto-optic material selectedfor example from the group consisting of Tb—Fe—Co and Gd—Tb—Fe.

In another aspect of the invention, the first metal alloy in the a layerof an optical recording medium may comprise copper, zinc, and silverwherein copper is present from about 0.01 a/o percent to about 10.0 a/opercent, zinc is present from about 0.01 a/o percent to 10.0 a/o, andthe remainder is silver.

In another aspect of the invention, a metal alloy in a layer of anoptical recording medium may comprise copper, titanium, and silver,wherein copper is present in about 0.01 a/o percent to about 10.0 a/opercent of the amount of silver present, and titanium is present fromabout 0.01 a/o percent to about 5.0 a/o percent of the amount of silverpresent in the alloy.

In another aspect of the invention, a metal alloy in a layer of anoptical recording medium may comprise silver; and at least one othermetal selected from the group consisting of gold, rhodium, ruthenium,osmium, iridium, platinum, palladium, and mixtures thereof, wherein atleast one of these metals is present from about 0.01 a/o percent toabout 5.0 a/o percent of the amount of silver present.

In another aspect of the invention, the metal alloy in a layer of anoptical recording medium may comprise silver, copper, and silicon,wherein copper is present from about 0.01 a/o percent to about 10.0 a/opercent of the amount of silver present, and silicon is present fromabout 0.01 a/o percent to about 5.0 a/o percent of the amount of silverpresent.

In still another aspect this invention is an optical informationrecording medium, comprising: a first substrate having a pattern offeatures in at least one major surface; a first recording layer adjacentthe feature pattern; and a first reflective layer adjacent to the firstrecording layer. The reflective layer includes a first metal alloy;wherein the first metal alloy comprises: silver; and at least one otherelement selected from the group consisting of copper, zinc, titanium,cadmium, lithium, nickel, cobalt, indium, aluminum, germanium, chromium,germanium, tin, beryllium, magnesium, manganese, antimony, gallium,silicon, boron, zirconium, molybdenum, and mixtures thereof, whereinsaid other elements are present from 0.01 a/o percent to 10.0 a/opercent of the amount of silver present. In another aspect of theinvention, the other elements of the aforementioned metal alloy arepresent from about 0.1 a/o percent to 5.0 a/o percent of the amount ofsilver present in the alloy.

In one aspect of the invention, the first recording layer of an opticalinformation recording medium may directly contact the first metal layer.

In another aspect of the invention, a metal alloy of an opticalrecording medium, may comprise silver, copper, and zinc wherein copperis present from about 0.01 a/o percent to 10.0 a/o percent of the amountof silver present, and zinc is present from about 0.01 a/o percent to10.0 a/o percent of the amount of silver present.

In another aspect of the invention, a metal alloy of a layer of anoptical recording medium is comprised of silver and at least one elementselected from the group consisting of gold, rhodium, ruthenium, osmium,iridium, platinum, palladium, and mixtures thereof, wherein the elementis present from about 0.01 a/o percent to 5.0 a/o percent of the amountof silver present.

In yet another aspect, the invention is an optical storage medium,comprising: a first substrate having a pattern of features in at leastone major surface; a semi-reflective layer adjacent a feature pattern,the semi-reflective layer including a metal alloy; the metal alloycomprising: silver; and copper; wherein the relationship between theamounts of silver and copper is defined by Ag_(x)Cu_(y), where0.90<x<0.999, 0.001<y<0.10; a second substrate having a pattern offeatures in at least one major surface; a high reflective layer adjacentthe feature pattern of the second substrate; and at least one spacerlayer, located between said first and second substrates.

The aforementioned medium may further include a second substrate havinga pattern of features in at least one major surface and a secondreflective layer adjacent the second substrate. The metal alloy may alsobe comprised of at least one additional element selected from the groupconsisting of silicon, cadmium, tin, lithium, nickel, cobalt, indium,chromium, antimony, gallium, boron, molybdenum, zirconium, beryllium,titanium, magnesium, wherein the elements are present from about 0.01a/o percent to 10.0 a/o percent of the amount of silver present.

In still another aspect of the invention, the first metal alloy in anoptical storage medium with both reflective and semi-reflective layers,comprising Ag_(x)Cu_(y,) where 0.90<x<0.999, 0.001<y<0.10,includesmanganese present from about 0.01 a/o percent to about 7.5 a/o percentof the amount of silver present.

In still another aspect of the invention, the metal alloy in an opticalstorage medium with both reflective and semi-reflective layers,comprising Ag_(x)Cu_(y), where 0.90<x<0.999, 0.001<y<0.10, includesmanganese present from about 0.01 a/o percent to about 5.0 a/o percentof the amount of silver present.

In still another aspect of the invention, the metal alloy in an opticalstorage medium with both reflective and semi-reflective layers,comprising Ag_(x)Cu_(y,) where 0.90<x<0.999, 0.001<y<0.10,includestitanium present from about 0.01 a/o percent to about 5.0 a/o percent ofthe amount of silver present.

In still another aspect of the invention, the metal alloy in an opticalstorage medium with both reflective and semi-reflective layers,comprising Ag_(x)Cu_(y,) where 0.90<x<0.999, 0.001<y<0.10,includessilicon present from about 0.01 a/o percent to about 5.0 a/o percent ofthe amount of silver present.

In another aspect of the invention, the semi-reflective layer of opticalstorage medium includes a metal alloy comprising Ag_(x)Cu_(y,) wherein0.95<x<0.999, 0.001<y<0.050.

In another aspect of the invention, the semi-reflective layer of anoptical storage medium directly contacts the first metal alloy of themedium.

In another aspect of the invention, an optical information recordingmedium, may further include a second substrate having a pattern offeatures in at least one major surface and spacer layer located betweenthe first and second substrates.

In one aspect, this invention is an optical storage medium with a firstsubstrate having a pattern of features in at least one major surface anda first reflective layer adjacent the feature pattern. The reflectivelayer is made of a silver and zinc alloy wherein the relationshipbetween the amount of silver and the amount of zinc is defined byAg_(x)Zn_(y,) where 0.85<x<0.9999 and 0.0001<y<0.15.

In another aspect, this invention is an optical storage medium with afirst substrate having a pattern of features in at least one majorsurface and a first reflective layer adjacent the feature pattern. Thereflective layer is made of a silver and aluminum alloy where therelationship between the amount of silver and the amount of aluminum isdefined by Ag_(x)Al_(z,) where 0.95<x<0.9999 and 0.0001<x<0.05.

In another aspect, this invention is an optical storage medium with afirst substrate having a pattern of features in at least one majorsurface and a first reflective layer adjacent the feature pattern. Thereflective layer is made of a silver and zinc and aluminum alloy wherethe relationship between the amount of silver and the amount of zinc andthe amount of aluminum is defined by Ag_(x)Zn_(y)Al_(z,) where0.80<x<0.998 and 0.001<y<0.15, and 0.001<z<0.05.

In another aspect, this invention is an optical storage medium with afirst substrate having a pattern of features in at least one majorsurface and a first reflective layer adjacent the feature pattern. Thereflective layer is made of a silver and manganese alloy where therelationship between the amount of silver and manganese is defined byAg_(x)Mn_(t,) where 0.925<x<0.9999 and 0.0001<t<0.075.

In another aspect, this invention is an optical storage medium with afirst substrate having a pattern of features in at least one majorsurface and a first reflective layer adjacent the feature pattern. Thereflective layer is made of a silver and germanium alloy wherein therelationship between the amount of silver and the amount of germanium isdefined by Ag_(x)Ge_(q,) where 0.97<x<0.9999 and 0.0001<q<0.03.

In another aspect, this invention is an optical storage medium with afirst substrate having a pattern of features in at least one majorsurface and a first reflective layer adjacent the feature pattern. Thereflective layer is made of a silver and copper and manganese alloywherein the relationship between the amount of silver and the amount ofcopper and the amount of manganese is defined by Ag_(x)Cu_(p)Mn_(t,)where 0.825<x<0.9998 and 0.0001<p<0.10, and 0.0001<t<0.075.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an optical storage system according to one embodiment of thisinvention.

FIG. 2 is an optical storage system according to another embodiment ofthis invention where an organic dye is used as a recording layer.

FIG. 3 is an optical storage system according to another embodiment ofthis invention with two layers of information pits where the playback ofboth layers is from one side.

FIG. 4 is an optical storage system according to another embodiment ofthis invention with three layers of information pits where the playbackof all three layers is from one side.

FIG. 5 is an optical storage system according to another embodiment ofthis invention where the system contains a rewritable information layer.

FIG. 6 is an optical storage system according to another embodiment ofthis invention where the system contains a rewritable information layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Specific language is used in the following description and examples topublicly disclose the invention and to convey its principles to others.No limits on the breadth of the patent rights based simply on usingspecific language are intended. Also included are any alterations andmodifications to the descriptions that should normally occur to one ofaverage skill in this technology.

As used in this specification the term “atomic percent” or “a/o percent”refers to the ratio of atoms of a particular element or group ofelements to the total number of atoms that are identified to be presentin a particular alloy. For example, an alloy that is 15 atomic percentelement “A” and 85 atomic percent element “B” could also be referencedby a formula for that particular alloy: A_(0.15)B_(0.85).

As used herein the term “of the amount of silver present” is used todescribe the amount of a particular additive that is included in thealloy. Used in this fashion, the term means that the amount of silverpresent, without consideration of the additive, is reduced by the amountof the additive that is present to account for the presence of theadditive in a ratio. For example, if the relationship between Ag and anelement “X” is Ag_(0.85) X_(0.15) (respectively 85 a/o percent and 15a/o percent) without the considering the amount of the additive that ispresent, and if an additive “B” is present at a level 5 atomic percent“of the amount of silver present”; then the relationship between Ag, X,and B is found by subtracting 5 atomic percent from the atomic percentof silver, or the relationship between Ag, X, and B is Ag_(0.80)X_(0.15) B_(0.05) (respectively 80 a/o percent silver, 15 a/o percent“X”, and 5 a/o percent “B”).

As used in this specification the term “adjacent” refers to a spatialrelationship and means “nearby” or “not distant”. Accordingly, the term“adjacent” as used in this specification does not require that items soidentified are in contact with one another and that they may beseparated by other structures. For example, referring to FIG. 5, layer424 is “adjacent” or “nearby” layer 422, just as layer 414 is “adjacent”or “nearby” layer 422.

Metal alloys for use in optical recording devices have been disclosed inU.S. Pat. Nos. 6,007,889; 6,280,811; 6,451,402 B1; and 6,544,616 B2, andthese patents are hereby incorporated by reference in their entirety.

This invention comprises multi-layer metal/substrate compositions thatare used as optical data storage media. One embodiment of this inventionis shown in FIG. 1 as optical data storage system 10. Optical storagemedium 12 comprises a transparent substrate 14, and a highly reflectivethin film layer or coating 20 on a first data pit pattern 19. An opticallaser 30 emits an optical beam toward medium 12, as shown in FIG. 1.Light from the optical beam that is reflected by thin film layer 20 issensed by detector 32, which senses modulations in light intensity basedon the presence or absence of a pit or land in a particular spot on thethin film layer. The disc is unique in that one of the alloys presentedbelow is deposited upon the information pits and lands and is used asthe highly reflective thin film 20. In one alternative (not shown), thedisc may be varied by attaching two optical storage media 12back-to-back, that is, with each transparent substrate 14 facingoutward.

Another embodiment of this invention is shown in FIG. 2 as optical datastorage system 110. Optical storage medium 112 comprises a transparentsubstrate 114, and a highly reflective thin film layer 120, over a layerof dye 122, placed over a first pattern 119. An optical laser 130 emitsan optical beam toward medium 112, as shown in FIG. 2. As discussedearlier, data is placed upon the disc by deforming portions of the dyelayer with a laser. Thereafter, the disc is played by light from theoptical beam, which is reflected by thin film layer 120 and sensed bydetector 132. Detector 132 senses modulations in light intensity basedon the presence or absence of a deformation in the dye layer. The discis unique in that one of the alloys presented below is deposited overthe dye layer 122 and is used as the highly reflective thin film orcoating 120. In one alternative (not shown), the disc may be varied byattaching two optical storage media 112 back-to-back, that is, with eachtransparent substrate 114 facing outward.

Another embodiment of this invention is shown in FIG. 3 as optical datastorage system 210. Optical storage medium 212 comprises a transparentsubstrate 214, a partially reflective thin film layer or coating 216 ona first data pit pattern 215, a transparent spacer layer 218, and ahighly reflective thin film layer or coating 220 on a second data pitpattern 219. An optical laser 230 emits an optical beam toward medium212, as shown in FIG. 3. Light from the optical beam that is reflectedby either thin film layer 216 or 220 is sensed by detector 232, whichsenses modulations in light intensity based on the presence or absenceof a pit in a particular spot on the thin film layers. The disc isunique in that one of the alloys presented below is deposited upon theinformation pits and lands and used as the highly reflective thin film220 or semi-reflective layer 216. In another alternative (not shown),the disc may be varied by attaching two optical storage media 212back-to-back, that is, with each transparent substrate 214 facingoutward. The attachment method could be by UV cured adhesive, hot meltadhesive or other type of adhesives.

Another embodiment of this invention is shown in FIG. 4 as optical datastorage system 310. Optical storage medium 312 comprises a transparentsubstrate 314, a partially reflective thin film layer or coating 316 orlayer “zero” on a first data pit pattern 315, a transparent spacer layer318, another partially reflective thin film layer or coating 320 orlayer “one” on a second data pit pattern 319, a second transparentspacer layer 322, and a highly reflective thin film layer or coating 324or layer “two” on a third pit pattern 323. An optical laser 330 emits anoptical beam toward medium 312, as shown in FIG. 4. Light from theoptical beam that is reflected by thin film layer 316, 320 or 324 isdetected by detector 332, which senses modulation in light intensitybased on the presence or absence of a pit in a particular spot on thethin film layers. The disc is unique in that any or all of the alloyspresented below can be deposited upon the information pits and lands andused as the highly reflective thin film or coating 324 or thesemi-reflective layer or coating 316 and 320. To playback theinformation on Layer 2, the light beam from laser diode 330 is goingthrough the transparent polycarbonate substrate, passing through thefirst semi-reflective Layer 0, and the second semi-reflective Layer 1and then reflected back from layer 2 to the detector 332. In anotheralternative (not shown), the disc may be varied by attaching two opticalstorage media 312 back-to-back, that is, with each transparent substrate314 facing outward. The attachment method could be by UV cured adhesive,hot melt adhesive or other type of adhesives.

Still another embodiment of this invention is shown in FIG. 5 as opticaldata storage system 410. Optical storage medium 412 comprises atransparent substrate or a transparent layer 414, a dielectric layer 416on a first data pit pattern 415, a recording layer 418 made of amaterial having a microstructure including domains or portions capableof repeatedly undergoing laser-induced transitions from a first state toa second state and back again (i.e., an optically re-recordable orrewritable layer), such as a phase change material or a magneto-opticmaterial, another dielectric material 420, a highly reflective thin filmlayer 422, and a transparent substrate or layer 424. As used in thisspecification, a dielectric material is a material that is an electricalinsulator or in which an electric field can be sustained with a minimumdissipation of power. The different layers 414, 416, 418, 420 and 422 ofthe optical storage medium 410 are preferably oriented so as to beadjacent with one another.

The optical recordable material may be for example, a magneto-opticmaterial selected from the group consisting of Tb—Fe—Co and Gd—Tb—Fe.

Commonly used phase change materials for the recording layer 418 includegermanium-antimony-tellurium (Ge—Sb—Te),silver-indium-antimony-tellurium (Ag—In—Sb—Te),chromium-germanium-antimony-tellurium (Cr—Ge—Sb—Te) and the like.Commonly used materials for the dielectric Layer 416 or 420 include zincsulfide-silica compound (ZnS.SiO₂), silicon nitride (SiN), aluminumnitride (AlN) and the like. Commonly used magneto-optic materials forthe recording layer 418 include terbium-iron-cobalt (Tb—Fe—Co) orgadolinium-terbium-iron (Gd—Tb—Fe). An optical laser 430 emits anoptical beam toward medium 412, as shown in FIG. 5. In the recordingmode for the phase change recordable optical medium, light from theoptical beam is modulated or turned on and off according to the inputdigital data and focused on the recording layer 418 with suitableobjective while the medium is rotated in a suitable speed to effectmicrostructural or phase change in the recording layer. In the playbackmode, the light from the optical beam that is reflected by the thin filmlayer 422 through the medium 412 is sensed by the detector 432, whichsenses modulations in light intensity based on the crystalline oramorphous state of a particular spot in the recording layers. The discis unique in that one of the alloys presented below is deposited uponthe medium and used as the highly reflective thin film 422. In anotheralternative (not shown), the disc may be varied by attaching two opticalstorage media 412 back-to-back, that is, with each transparent substrateor coating 414 facing outward. The attachment method could be by UVcured adhesive, hot melt adhesive or other type of adhesives.

As shown in FIG. 5, if transparent substrate 414 is about 1.2 mm thickmade of injection molded polycarbonate with continuous spirals ofgrooves and lands, 424 is a UV cured acrylic resin 3 to 15 micron thickacting as a protective layer with the playback laser 430 at 780 to 820nanometer, and rewritable layer 418 is a phase change material of atypical composition such as Ag—In—Sb—Te, it is a compact disc-rewritabledisc structure, commonly known as a CD-RW. To record and readinformation, phase change discs utilize the recording layer's ability tochange from an amorphous phase with low reflectivity (dark) to acrystalline phase with high reflectivity (bright). Before recording, thephase change layer is in a crystalline state. During recording, a laserbeam with high power focused on the recording layer will heat the phasechange material to high temperature and when the laser is turned off,the heated spot will cool off very quickly to create an amorphous state.Thus a series of dark spots of amorphous states are created according tothe input data of turning the focused laser beam on and off. These onand off correspond to “0” and “1” of a digital data stream.

In reading, a low laser power is used to focus on and read the dark orbright spots along the track of the disc to play back the recordedinformation. To erase, an intermediate laser power is used to focus onthe grooves or tracks with the disc spinning so that an intermediatetemperature of the focused spots is reached. After the laser is moved toanother location, the spots cool to room temperature forming acrystalline structure of high reflectivity. This returns the recordinglayer to its original or erased state. The change of the spots' statefrom amorphous to crystalline is very reversible, thus many record anderase cycles can be accomplished and different data can be repeatedlyrecorded and read back without difficulty.

If transparent substrate 414 is about 0.5 to 0.6 mm thick made ofinjection molded polycarbonate with continuous spirals of grooves andlands, 416 and 420 are dielectric layers typically made of ZnS.SiO₂, 418is made of a phase change material such as Ag—In—Sb—Te or Ge—Sb—Te, 422is made of a silver alloy of the current invention, and 424 is a UVcured resin bonding another half of the same structure as depicted inFIG. 5., and the structure is used with a read and write laser 430 at630 to 650 nanometer wavelength, then it is a digital versatile discwith rewritable capability, commonly referred to as DVD+RW. Somepreferred phase-changeable materials include materials from thefollowing series: As—Te—Ge, As—In—Sb—Te, Te—Ge—Sn, Te—Ge—Sn—O, Bi—Ge,Bi—Ge—Sb, Bi—Ge—Te, Te—Se, Sn—Te—Se, Te—Ge—Sn—Au, Ge—Sb—Te, Sb—Te—Se,In—Se—Tl, In—Sb, In—Sb—Se, In—Se—Tl—Co, Cr—Ge—Sb—Te and Si—Te—Sn, whereAs is arsenic, Bi is Bismuth, Te is tellurium, Ge is germanium, Sn istin, O is oxygen, Se is selenium, Au is gold, Sb is antimony, In isindium, Tl is thallium, Co is cobalt, and Cr is chromium. In this discconfiguration, the highly reflective layer 422 needs not only highreflectivity at 650 nanometer wavelength and high thermal conductivity,but also high corrosion resistance in the presence of ZnS.SiO₂.Conventional aluminum alloy does not have high enough reflectivity norhigh enough thermal conductivity. Pure silver or other conventionalsilver alloys do not have either high corrosion resistance or highreflectivity and high thermal conductivity. Thus it is another objectiveof the current invention to provide a series of silver alloys that canmeet the requirements for this application.

Another embodiment of the current invention is shown in FIG. 6, arewritable type optical information storage system 510. Transparentcover layer 514 is approximately 0.1 mm thick. Dielectric layers 516 and520 are preferably made of ZnS.SiO₂ and serve as a protective layer forthe rewritable layer or phase change layer 518. Rewritable layer 518 ispreferably formed from Ag—In—Sb—Te or the like. Highly reflective layer522 is preferably formed from a silver alloy, such as disclosed herein.Transparent substrate 524 is preferably approximately 1.1 mm inthickness with continuous spiral tracks of grooves and lands usuallymade with polycarbonate resin. Laser 530 preferably has a wavelength ofabout 400 nm with associated optics to focus the laser beam ontorecording layer 518. The reflected laser beam is received by thedetector 532, which preferably includes associated data processingcapability to read back the recorded information. System 510 issometimes called a “Digital Video Recording System” or DVR, and it isdesigned to record high definition TV signal. The principle of operationof optical information storage system 510 is similar to that of a CD-RWdisc except that the recording density is considerably higher, thestorage capacity of a 5-inch diameter disc is approximately 20gigabytes. Again the performance of the disc stack depends on a layer522, that is highly reflective at 400 nm wavelength, with high corrosionresistance and very high thermal conductivity. Conventional reflectivelayers such as aluminum, gold or copper all have difficulty meetingthese requirements. Thus it is another objective of the currentinvention to provide a silver alloy reflective layer that is capable ofmeeting these demanding requirements.

As used herein, the term “reflectivity” refers to the fraction ofoptical power incident upon transparent substrate 14, 114, 214, 314, 414or 514 which, when focused to a spot on a region of layer 20, 120, 216,220, 316, 320, 324, 422 or 522 could in principle, be sensed by aphotodetector in an optical readout device. It is assumed that thereadout device includes a laser, an appropriately designed optical path,and a photodetector, or the functional equivalents thereof.

This invention is based on the inventor's discovery that, a particularsilver-based alloy provides sufficient reflectivity and corrosionresistance to be used as the reflective or the semi-reflective layer inan optical storage medium, without the inherent cost of a gold-basedalloy or the process complication of a silicon-based material. In oneembodiment, silver is alloyed with a comparatively small amount of zinc.In this embodiment, the relationship between the amounts of zinc andsilver ranges from about 0.01 a/o percent (atomic percent) to about 15a/o percent zinc and from about 85 a/o percent to about 99.99 a/opercent silver. But preferably in respect to each metal, the alloy hasfrom about 0.1 a/o percent to about 10.0 a/o percent zinc and from about90.0 a/o percent to about 99.9 a/o percent silver.

In another embodiment, the silver is alloyed with a comparatively smallamount of aluminum. In this embodiment, the relationship between theamounts of aluminum and silver ranges from about 0.01 a/o percent(atomic percent) to about 5 a/o percent aluminum and from about 95 a/opercent to about 99.99 a/o percent silver. But preferably in respect toeach metal, the alloy has from about 0.1 a/o percent to about 3.0a/opercent aluminum and from about 97 a/o percent to about 99.9a/o percentsilver.

In another embodiment of the present invention, the silver-based, binaryalloy systems as mentioned above are further alloyed with cadmium (Cd),lithium (Li), or manganese (Mn). If one or more of these metals replacesa portion of the silver in the alloy, the corrosion resistance of theresultant thin film will likely increase; however, the reflectivity willalso likely decrease. The amount of cadmium, lithium, or manganese thatmay favorably replace some of the silver in the binary alloy rangesfrom; about 0.01 a/o percent to about 20 a/o percent of the amount ofsilver present for cadmium; from about 0.01 a/o percent to about 10 a/opercent, or even, to about 15 a/o percent of the amount of silverpresent for lithium; and from about 0.01 a/o percent to about 7.5 a/opercent of the amount of silver present for manganese.

In still another embodiment of the present invention, the silver-based,zinc and aluminum binary alloy systems as mentioned above are furtheralloyed with a precious metal such as gold (Au), rhodium (Rh), copper(Cu), ruthenium (Ru), osmium (Os), iridium (Ir), platinum (Pt),palladium (Pd), and mixtures thereof, which may be added to the abovebinary alloys with the preferable range of precious metal to be about0.01 a/o to 5.0 a/o percent of the amount of silver present. In additionto precious metals, the above alloys may be still further alloyed with ametal such as titanium (Ti), nickel (Ni), indium (In), chromium (Cr),germanium (Ge), tin (Sn), antimony (Sb), gallium (Ga), silicon (Si),boron (B), zirconium (Zr), molybdenum (Mo), and mixtures thereof. Inrelation to the amount of silver that is present in the aforementionedsilver alloys, the amount of these metals that may preferably be addedranges from about 0.01 a/o percent to about 5.0 a/o of the amount ofsilver present.

In another embodiment, silver is alloyed with at least one otherelement, selected from the group of elements including copper, silicon,cadmium, tin, lithium, nickel, cobalt, indium, chromium, antimony,gallium, boron, molybdenum, zirconium, beryllium, titanium andmagnesium, wherein said other elements are present from about 0.01 a/opercent to 10.0 a/o percent of the amount of silver present. In onepreferred embodiment, the non-silver element is present in the alloy inthe amount of about 0.1 a/o percent to 5.0 a/o percent.

In still another embodiment, the silver is alloyed with a comparativelysmall amount of both zinc and aluminum. In this embodiment, therelationship between the amounts of zinc, aluminum and silver rangesfrom about 0.1 a/o percent to about 15 a/o percent zinc, from about 0.1a/o percent to about 5 a/o percent aluminum, and from about 80 a/opercent to about 99.8 a/o percent silver. But preferably with respect toeach metal, the alloy has from about 0.1 a/o percent to about 5.0 a/opercent zinc, from about 0.1 a/o percent to about 3.0 a/o percentaluminum, and from about 92.0 a/o percent to about 99.8 a/o percentsilver.

In yet another embodiment of the present invention, the silver-basedzinc-aluminum ternary alloy system as mentioned above is further alloyedwith a fourth metal. The fourth metal may include manganese or nickel.If one or a mixture of these metals replaces a portion of the silver inthe alloy, the corrosion resistance of the resultant thin film willlikely increase; however, the reflectivity will also likely decrease.The amount of manganese or nickel that may favorably replace some of thesilver in the above ternary alloys ranges from, about 0.01 a/o percentto about 7.5 a/o percent of the amount of silver present for manganese,with a preferable range being between about 0.01 a/o percent and about5.0 a/o percent of the amount of silver present. The amount of nickelmay range from between about 0.01 a/o percent to about 5.0 a/o percentof the amount of silver present with a preferable range being betweenfrom about 0.01 a/o percent and about 3.0 a/o percent of the amount ofsilver present.

In still another embodiment of the present invention, the silver-basedzinc-aluminum ternary alloy system as mentioned above is further alloyedwith a precious metal such as gold, rhodium, copper, ruthenium, osmium,iridium, platinum, palladium, and mixtures thereof, which may be addedto the above ternary alloys with the preferable range of precious metalto be about 0.01 a/o to 5.0 a/o percent of the amount of silver present.In addition to the precious metals, the above alloys may also be alloyedwith a metal such as titanium, nickel, indium, chromium, germanium, tin,antimony, gallium, silicon, boron, zirconium, molybdenum, and mixturesthereof. In relation to the amount of silver that is present in theabove silver alloy system, the amount of such metals that may bepreferably added ranges from about 0.01 a/o percent to about 5.0 a/opercent of the amount of silver present.

In another embodiment, the silver is alloyed with a comparatively smallamount of manganese. In this embodiment, the relationship between theamounts of manganese and silver ranges from about 0.01 a/o percent toabout 7.5 a/o percent manganese and from about 92.5 a/o percent to about99.99 a/o percent silver. But preferably in respect to each metal, thealloy has from about 0.1 a/o percent to about 5 a/o percent manganeseand from about 95 a/o percent to about 99.9 a/o percent silver.

In yet another embodiment of the present invention, the silver-basedbinary manganese alloy system as mentioned above is further alloyed witha third metal. The third metal may include cadmium, nickel, lithium andmixtures thereof. If one or a mixture of these metals replaces a portionof the silver in the alloy, the corrosion resistance of the resultantthin film will likely increase; however, the reflectivity will alsolikely decrease. In relation to the amount of silver that is present inthe above binary alloy systems, the amount of cadmium may be range fromabout 0.01 a/o percent to about 20 a/o percent of the alloy of theamount of silver present, the amount of nickel may range from betweenabout 0.01 a/o percent to about 5.0 a/o percent of the amount of silverpresent, and the amount of lithium may range from about 0.01 a/o percentto about 10.0 a/o percent of the amount of silver present.

In still another embodiment of the present invention, the aforementionedsilver-based manganese alloy system is further alloyed with a preciousmetal such as gold, rhodium, copper, ruthenium, osmium, iridium,platinum, palladium, and mixtures thereof, which may be added to thesebinary alloys, the preferred range of precious metal added is about 0.01a/o to 5.0 a/o percent of the amount of silver present. In addition tothe precious metals, the aforementioned alloys may also be alloyed witha metal such as titanium, indium, chromium, germanium, tin, antimony,gallium, silicon, boron, zirconium, molybdenum, and mixtures thereof. Inrelation to the amount of silver that is present in the above silveralloy system, the amount of the latter metal(s) that may preferably beadded ranges from about 0.01 a/o percent to about 5.0 a/o percent of theamount of silver present.

In still another embodiment, silver is alloyed with a comparativelysmall amount of germanium. In this embodiment, the relationship betweenthe amounts of germanium and silver ranges from about 0.01 a/o percentto about 3.0 a/o percent germanium and from about 97.0 a/o percent toabout 99.99 a/o percent silver. But preferably in respect to each metal,the alloy has from about 0.1 a/o percent to about 1.5 a/o percentgermanium and from about 98.5 a/o percent to about 99.9 a/o percentsilver.

In yet another embodiment of the present invention, the silver-basedgermanium alloy system as mentioned above is further alloyed with athird metal. The third metal may include manganese or aluminum. If oneor a mixture of these metals replaces a portion of the silver in thealloy, the corrosion resistance of the resultant thin film will likelyincrease; however, the reflectivity will also likely drop. In relationto the amount of silver that is present in the above binary alloysystem, the amount of manganese may be range from about 0.01 a/o percentto about 7.5 a/o percent of the amount of silver present and the amountof aluminum may range from between about 0.01 a/o percent to about 5.0a/o percent of the amount of silver present.

In still another embodiment of the present invention, the aforementionedsilver-based germanium alloy system is further alloyed with a preciousmetal such as gold, rhodium, copper, ruthenium, osmium, iridium,platinum, palladium, and mixtures thereof, which may be added to theabove binary alloys, the preferable range of precious metals added isabout 0.01 a/o to 5.0 a/o percent of the amount of silver present. Inaddition to the precious metals, the alloys may also be alloyed with ametal such as zinc, cadmium, lithium, nickel, titanium, zirconium,indium, chromium, tin, antimony, gallium, silicon, boron, molybdenum,and mixtures thereof. In relation to the amount of silver present in theabove silver alloy system, the amount of these metals that may bepreferably added ranges from about 0.01 a/o percent to about 5.0 a/opercent of the amount of silver present.

In still another embodiment, the silver is alloyed with a comparativelysmall amount of both copper and manganese. In this embodiment, therelationship between the amounts of copper, manganese and silver rangesfrom about 0.01 a/o percent to about 10 a/o percent copper, from about0.01 a/o percent to about 7.5 a/o percent manganese, and from about 82.5a/o percent to about 99.98 a/o percent silver. But preferably in respectto each metal, the alloy has from about 0.1 a/o percent to about 5.0 a/opercent copper, from about 0.1 a/o percent to about 3.0 a/o percentmanganese, and from about 92.0 a/o percent to about 99.8 a/o percentsilver.

In yet another embodiment of the present invention, the silver-basedcopper-manganese alloy system as mentioned above is further alloyed afourth metal. The fourth metal such as aluminum, titanium, zirconium,nickel, indium, chromium, germanium, tin, antimony, gallium, silicon,boron, molybdenum, and mixtures thereof. In relation to the amount ofsilver that is present in the above silver alloy system, the amount offourth metal that may be preferably added ranges from about 0.01 a/opercent to about 5.0 a/o percent of the amount of silver present.

The optical properties of these silver alloys as thin film, with athickness in the range of 8 to 12 nanometers, for the semi reflectivelayer of DVD-9 dual layer discs are illustrated in Table I in thefollowing. As mentioned in U.S. Pat. No. 5,464,619 assigned toMatsushita Electric and U.S. Pat. No. 5,726,970 assigned to Sony, in adual layer optical disc structure (as illustrated in FIG. 3 and in TableI), the relationship between R₀ the reflectivity of Layer “0” or 216 andR₁ the reflectivity of Layer “1” or 220 is given by R₀=R₁T₀ ². Where thereflectivity of Layer “1” or 220 is measured from outside the disc, andthe transmission of Layer “0” is given as T₀. When the thickness oflayer “0” is optimized for balanced signal and reflectivity, and Layer“1” is an conventional aluminum alloy, at 50 to 60 nanometers, thebalanced reflectivity of various silver alloys is shown in Table I. InTable I, R is the reflectivity of the thin film achievable at athickness of 60 nanometer or greater, at a wavelength of 650 nanometerif used as Layer “1” or the high reflectivity layer of DVD-9 or anyother high reflectivity application in an optical information storagemedium. All compositions in the table I are given in atomic percent.TABLE I Balance of reflectivity of Layer 0 and Layer 1 of DVD-9 duallayer disc for various silver alloy Layer 0 and typical aluminum alloyLayer 1. Composition T₀ R₀ R₁ R Ag—13.0% Zn 0.47 0.185 0.183 0.80Ag—6.0% Zn 0.52 0.22 0.224 0.92 Ag—4.0% Zn 0.53 0.23 0.233 0.93 Ag—10.3%Cd 0.51 0.22 0.216 0.91 Ag—14.5% Li 0.53 0.23 0.232 0.93 Ag—4.3% Al 0.470.18 0.183 0.80 Ag—1.5% Al 0.53 0.23 0.234 0.93 Ag—2.0% Ni 0.54 0.2410.241 0.94 Ag—1.0% Ni 0.545 0.247 0.246 0.95 Ag—3.1% Mn 0.51 0.216 0.2140.91 Ag—1.5% Mn 0.54 0.243 0.242 0.94 Ag—0.4% Ti 0.49 0.198 0.197 0.88Ag—1.0% Zr 0.52 0.229 0.224 0.93

In still another embodiment of the present invention, the sputteringtarget and the thin film on the optical information storage medium is asilver alloy with a comparatively small addition of aluminum as analloying element. In this embodiment, the relationship between theamounts of silver and aluminum ranges from about 0.01 a/o percent toabout 5.0 a/o percent aluminum and from about 95.0 a/o percent to about99.99 a/o percent silver. But preferably from about 0.1 a/o percent toabout 3.0 a/o percent aluminum, and from about 97.0 a/o percent to about99.9 a/o percent silver. This silver and aluminum binary alloy can befurther alloyed with zinc, cadmium, lithium, manganese, nickel, titaniumand zirconium or mixtures of these metals. In relation to the amount ofsilver that is present in the above silver and aluminum binary alloy,the amount of the above-identified metal that may be preferably addedranges from 0.01 a/o percent to about 5.0 a/o percent of the silvercontent.

For the convenience of the reader, the following are some combinationsof silver alloys, wherein the alloying elements, which may be preferablyalloyed with silver, are identified by their periodic table symbols:Ag+Zn, or Ag+Cd, or Ag+Li, or Ag+Al, or Ag+Ni, or Ag+Mn, or Ag+Ti, orAg+Zr, or Ag+Pd+Zn, or Ag+Pt+Zn, or Ag+Pd+Mn, or Ag+Pt+Mn, or Ag+Zn+Li,or Ag+Pt+Li, or Ag+Li+Mn, or Ag+Li+Al, or Ag+Ti+Zn, or Ag+Zr 30 Ni, orAg+Al+Ti, or Ag+Pd+Ti or Ag+Pt+Ti, or Ag 30 Ni+Al, or Ag+Mn+Ti, orAg+Zn+Zr, or Ag+Li+Zr, or Ag+Mn+Zn, or Ag+Mn+Cu, or Ag+Pd+Pt+Zn orAg+Pd+Zn+Mn, or Ag+Zn+Mn+Li, or Ag+Cd+Mn+Li, or Ag+Pt+Zn+Li, orAg+Al+Ni+Zn, or Ag+Al+Ni+Ti, or Ag+Zr+Ti+Cd, or Ag+Zr+Ni+Li, orAg+Zr+Ni+Al, or Ag+Pt+Al+Ni, or Ag+Pd+Zn+Al, or Ag+Zr+Zn+Ti, orAg+Ti+Ni+Al.

In another embodiment of the present invention, silver can be alloyedadditionally with indium, chromium, nickel, germanium, tin, antimony,gallium, silicon, boron, zirconium, and molybdenum or mixture of theseelements. In relation to the amount of silver that is present in thealloy systems, the amount of the above-identified elements that may beadded ranges from about 0.01 a/o percent to about 5.0 a/o percent of thesilver content. But more preferably, the amount of alloying elementsadded to silver may range from about 0.1 a/o percent to about 3.0 a/opercent. This is further illustrated in Table II for an opticalinformation storage medium as presented in FIG. 3. All the opticalproperty symbols in Table II have the same meaning as the same symbolsas those used in Table I. TABLE II Balance of reflectivity of Layer 0and Layer 1 of DVD-9 dual layer disc for various silver alloy Layer 0and typical aluminum alloy Layer 1. Composition T₀ R₀ R₁ R Ag—2.5% In0.500 0.212 0.208 0.91 Ag—1.2% Cr 0.535 0.243 0.238 0.94 Ag—0.7% Ge0.515 0.220 0.220 0.92 Ag—1.0% Sn 0.504 0.216 0.211 0.92 Ag—0.5% Sb0.520 0.224 0.224 0.93 Ag—3.0% Ga 0.475 0.195 0.187 0.86 Ag—1.5% Si0.490 0.202 0.199 0.90 Ag—1.2% B 0.513 0.247 0.218 0.92 Ag—0.8% Mo 0.5150.220 0.218 0.92

It is well understood in the art, that the compositions listed in TableI and Table II can also be used as the high reflectivity layer (Layer 1)in prerecorded dual layer optical disc structures such as DVD-9, DVD-14or DVD-18, in a tri-layer optical disc structure as illustrated in FIG.4, in a recordable optical disc such as DVD-R, in a rewritable opticaldisc such as DVD-RAM, or DVD-RW, or as the one illustrated in FIG. 5.

For the convenience of the reader, the following are some silver alloys,where the alloying elements, that may preferably be alloyed with silverare identified by their periodic table symbols; Ag+In, or Ag+Cr, orAg+Ge, or Ag+Sn, or Ag+Sb, or Ag+Ga, or Ag+Si, or Ag+B, or Ag+Mo, orAg+In+Cr, or Ag+Cr+Ge, or Ag+Cr+Sn, or Ag+Cr+Sb, or Ag+Cr+Si, orAg+Si+In, or Ag+Si+Sb, or Ag+Si+B, or Ag+Si+Mo, or Ag+Mo+In, orAg+Mo+Sn, or Ag+Mo+B, or Ag+Mo+Sb, or Ag+Ge+B, or Ag+In+Cr+Ge, orAg+Cr+Sn+Sb, or Ag+Ga+Si+Mo, or Ag+Cr+Si+Mo, or Ag+B+Mo+Cr, orAg+In+Sb+B, or Ag+Cr+Si+B, Ag+Ga+Ge+Cr, or Ag+Si+Ge+Mo or Ag+Sb+Si+B, orAg+Cr+Si+In, or Ag+Si+Cr+Sn.

The optical properties of a few of the ternary silver alloys of thepresent invention are further illustrated in Table III. In Table III,which shows the reflectivity and transmission of a thin film, layerzero, with a thickness of about 8 to 12 nm, in a DVD-9 dual layer discconstruction. The meaning of each symbol is the same as in Table I.TABLE III Balance of reflectivity of Layer 0 and Layer 1 of DVD-9 duallayer disc for various ternary silver alloy layer 0 and typical aluminumalloy Layer 1. Composition T₀ R₀ R₁ R Ag—1.2% Pd—1.4% Zn 0.54 0.2450.242 0.95 Ag—0.8% Cu—1.5% Mn 0.535 0.240 0.238 0.94 Ag—1.5% Al—1.0% Mn0.50 0.213 0.208 0.91 Ag—1.0% Cu—0.3% Ti 0.50 0.210 0.207 0.90 Ag—1.2%Al—1.3% Zn 0.53 0.224 0.233 0.93 Ag—1.0% Ge—0.7% Al 0.49 0.203 0.2010.89 Ag—1.2% Sb—0.3% Li 0.47 0.187 0.183 0.83

In another embodiment of the current invention, the thin film on anoptical information storage medium is, silver alloyed with acomparatively small amount of at least one other element selected fromthe group consisting of copper, silicon, cadmium, tin, lithium, nickel,cobalt, indium, chromium, antimony, gallium, boron, molybdenum,zirconium, beryllium, titanium and magnesium. The amount of otherelements that may be alloyed with silver ranges from about 0.01 a/opercent to about 10.0 a/o percent. And more preferably, the amount ofthe other element present in the silver based alloy ranges from about0.1 a/o percent to about 5.0 a/o percent, of the amount of silverpresent.

In another embodiment of the current invention, the thin film on anoptical information storage medium is, silver alloyed with copper andzinc. The amount of Cu present in the alloy ranges from about 0.01 a/opercent to about 10.0 a/o percent; and the amount of zinc present rangesfrom about 0.01 a/o percent to about 10.0 a/o percent, of the silverpresent in the alloy.

In another embodiment of the current invention, the thin film on anoptical information storage medium is, silver alloyed with copper andtitanium. The amount of Cu present in the alloy ranges from about 0.01a/o percent to about 10.0 a/o percent; and the amount of titaniumpresent in the alloy ranges from about 0.01 a/o percent to about 5.0 a/opercent, of the amount of silver present.

In another embodiment of the current invention, the thin film on anoptical information storage medium is, silver alloyed with at least oneother metal selected from the group including gold, rhodium, ruthenium,osmium, iridium, platinum, palladium, and mixtures thereof. The amountof the other metal present in the silver based alloy ranges from about0.01 a/o percent to about 5.0 a/o percent of the amount of silverpresent.

In another embodiment of the current invention, the thin film on anoptical information storage medium is, silver alloyed with copper, andsilicon. The amount of copper in the alloy ranges from about 0.01 a/o toabout 10.0 a/o percent, of the amount of silver present in the alloy.The amount of silicon present in the alloy ranges from about 0.01 a/o toabout 5.0 a/o percent of the amount of silver present.

In still another embodiment of the current invention, the thin film onan optical information storage medium is, silver alloyed with at leastone of the following elements selected from the group including; copper,zinc, titanium, cadmium, lithium, nickel, cobalt, indium, aluminum,germanium, chromium, germanium, tin, beryllium, magnesium, manganese,antimony, gallium, silicon, boron, zirconium, molybdenum, and mixturesthereof. The amount of the elements alloyed with silver ranges fromabout, 0.01 a/o percent to about 10.0 a/o percent of the amount ofsilver present. In one preferred embodiment the amount of the otherelement alloyed with silver ranges from about 0.1 a/o to about 5.0 a/opercent of the amount of silver present.

In another embodiment of the current invention, the thin film on anoptical information storage medium is, silver alloyed with copper andzinc. The amount of copper in the alloy ranges from about 0.01 a/o toabout 10.0 a/o percent, of the amount of silver present in the alloy.And the amount of zinc in the alloy ranges from about 0.01 a/o to about10.0 a/o percent, of the amount of silver present in the alloy.

In still another embodiment of the current invention, the thin film onan optical information storage medium is, silver alloyed with at leastone element selected from the group including gold, rhodium, ruthenium,osmium, iridium, platinum, palladium, and mixtures thereof. The amountof the element present in the alloy ranges from about 0.01 a/o to about5.0 a/o percent, of the amount of silver present in the alloy.

In yet another embodiment of invention, the thin film on an opticalinformation storage medium is a silver copper alloy defined byAg_(x)Cu_(y.) The amount of silver present in the alloy is given by avalue of x, where x is in the range of about 0.90 to about 0.999. Andthe amount of Cu in the alloy is given by a value of y, and y is in therange of about 0.001 to about 0.01.

In one preferred embodiment of the invention, the amount of silver inthe alloy is given by a value of x in the range of about 0.95 to about0.999, and the amount of Cu in the alloy is given by a value of y, inthe range of about 0.001 to about 0.050.

In yet another embodiment of the current invention, the thin film on anoptical information storage medium is, silver alloyed with copper, andat least one other element selected from the group including silicon,cadmium, tin, lithium, nickel, cobalt, indium, chromium, antimony,gallium, boron, molybdenum, zirconium, beryllium, titanium, magnesium.The amount of the other elements present in the alloy ranges from 0.01a/o percent to about 10.0 a/o percent, of the amount of silver present.

In still another embodiment of the current invention, the thin film onan optical information storage medium is silver alloyed with copper andmanganese. The amount of copper in the alloy ranges from about 0.001 toabout 0.01 a/o; the amount of manganese present in the alloy ranges fromabout 0.01 a/o to about 7.5 a/o percent, of the amount of silverpresent. In another preferred embodiment of the invention the amount ofmanganese present in the alloy ranges from about 1.01 a/o to about 5.0a/o percent, of the amount of silver present.

In another embodiment of the current invention, the thin film on anoptical information storage medium is, silver alloyed with copper andtitanium. The amount of copper present in the alloy ranges from about0.001 to about 0.01 a/o, and the amount of titanium present in the alloyranges from about 0.01 a/o to about 5.0 a/o percent, of the amount ofsilver present.

In still another embodiment of the current invention, the thin film onan optical information storage medium is, silver alloyed with copper andsilicon. The amount of copper in the alloy is in the range of about0.001 to about 0.01 a/o, and the amount of silicon in the alloy rangesfrom about 0.01 a/o to about 5.0 a/o percent, of the amount of silverpresent.

In still another embodiment of the current invention, the sputteringtarget and the thin film on an optical information storage medium is,silver alloyed with a comparatively, small amount of copper and otherelements selected from the group consisting of: aluminum, nickel,manganese, titanium, zirconium, indium, chromium, germanium, tin,antimony, gallium, silicon, boron, molybdenum and mixtures thereof. Inthis embodiment, the relationship between the amounts of silver andcopper ranges from about 0.01 a/o percent to about 5.0 a/o percentcopper and from about 95.0 a/o percent to about 99.99 a/o percentsilver. But preferably from about 0.1 a/o percent to about 3.0 a/opercent copper, and from about 97.0 a/o percent to about 99.9 a/opercent silver. In relationship to the amount of silver that is presentin the alloy system, the amount of the above-identified elements thatmay be added ranges from 0.01 a/o percent to about 5.0 % of the silvercontent. But more preferably, the amount of alloying elements added tosilver may ranges from about 0.1 a/o percent to about 3.0 a/o percent.As data presented in Table I, II and III indicated, if the individualalloy addition to silver is more than 5.0 a/o percent, the balancedreflectivity between layer zero and layer one in the DVD-9 dual layerdisc structure is likely to be lower than the DVD specification of 18percent, therefore not composition with utility.

Having presented the preceding compositions for the thin film materials,it is important to recognize that both the manufacturing process of thesputtering target and the process to deposit the target material into athin film play important roles in determining the final properties ofthe film. To this end, a preferred method of making the sputteringtarget will now be described. In general, vacuum melting and casting ofthe alloys or melting and casting under protective atmosphere, arepreferred to minimize the introduction of other unwanted impurities.

Afterwards, the as-cast ingot should undergo a cold or hot workingprocess to break down the segregated and the nonuniform as-castmicrostructure. One preferred method is cold or hot forging or cold orhot uniaxial compression with a more than 50 percent of size reduction,followed by annealing to recrystallize the deformed material into fineequi-axed grain structure with preferred texture of <1,1,0> orientation.This texture promotes directional sputtering in a sputtering apparatusso that more of the atoms from the sputtering target will be depositedonto the disc substrates for more efficient use of the target material.

Alternatively, a cold or hot multi-directional rolling process with morethan a 50 percent size reduction can be employed, followed by annealing,to promote a random oriented microstructure in the target followed bymachining the target to a final shape and size suitable for a givensputtering apparatus. A target, with a more random crystal orientation,will ejection atoms more randomly during sputtering, and will produce adisc substrate with a more uniform distribution and thickness.

Depending on the application, different discs' optical and other systemrequirements, either a cold or hot forging or a cold or hotmulti-directional rolling process can be employed in the targetmanufacturing process to optimize, the optical and other performancerequirements of, the thin film for use in a given application.

The alloys of this invention can be deposited using the well-knownmethods described earlier including, for example sputtering, thermalevaporation or physical vapor deposition, and possibly electrolytic orelectroless plating processes. The thin film alloy's reflectivity canvary depending on the method of application. Any application method thatadds impurities to, or changes the surface morphology of, the thin filmlayer on the disc could conceivably, lower the reflectivity of thelayer. But to a first order of approximation, the reflectivity of thethin film layer on the optical disc is primarily determined by thestarting material of the sputtering target, evaporation source material,or the purity and composition of the electrolytic and electrolessplating chemicals used.

It should be understood that the reflective layer of this invention canbe used for future generations of optical discs that use a reading laserof a shorter wavelength, for example, a reading laser with a wavelengthof 650 nanometers or shorter.

It should also be understood that, if the reflective film is reduced toa thickness of approximately 5 to 20 nanometers, a semi-reflective filmlayer can be formed from the alloys of this invention that havesufficient light transmittance for use in dual-layer DVD or dual layerblue-ray optical disc applications.

EXAMPLES Example 1

A silver based alloy with about 1.2 atomic percent chromium andapproximately 1.0 atomic percent zinc, at a thickness of about 60-100nanometers, will have a reflectivity of approximately 94 to 95 percentat a wavelength of 800 nanometers and a reflectivity of approximately 93to 94 percent at a wavelength of 650 nanometers and a reflectivity ofapproximately 86 to 88 percent at a wavelength of 400 nanometers.

Example 2

A silver-rich alloy with 1.5 a/o percent of manganese, and 0.8 a/opercent of copper will have a reflectivity of approximately 94 to 95percent at 650 nanometers wavelength. If the thickness of the thin filmis reduced to the 8 to 12 nanometers range, the reflectivity will bereduced to the range of 18 to 30 percent applicable for use as a DVD-9'ssemi-reflective layer. Adding a low concentration of deoxidizer such aslithium can further simplify the manufacturing process of the startingmaterial of the thin film. As silver has a tendency to dissolve someoxygen in the solid state, which tends to lower the reflectivity of thealloy, the added lithium will react with the oxygen and lessen thedegree of oxygen's impact to reflectivity. The desirable range oflithium is in the approximate range of 0.01 percent to 5.0 atomicpercent, with the preferred range from about 0.1 to 1.0 a/o percent.

Example 3

A silver based alloy with about 0.5 a/o percent of nickel and about 0.5a/o percent of zinc, about 60-70 nanometers thick, will have areflectivity of approximately 95 percent at a wavelength of about 650nanometers. It is suitable for any high reflectivity application in anoptical information storage medium.

Example 4

A silver based alloy sputtering target with a composition of about 1.0a/o percent manganese, 0.3 a/o percent titanium and the balance silveris employed to produce the semi-reflective layer of a DVD-9 dual layerdisc using the following procedure. On top of a transparentpolycarbonate half disc approximately 0.6 millimeters thick and 12centimeter in diameter with information pits injection molded from asuitable stamper, a semi-reflective thin film or layer “zero” of silverbased alloy approximately 10 to 11 nanometers thick is deposited orcoated, in a magnetron sputtering machine. On top of another transparentpolycarbonate half disc approximately 0.6 millimeter thick withinformation pits injection molded from a suitable stamper, a highreflectivity thin film or layer “one, of and aluminum based alloyapproximately 55 nanometers thick is deposited using a suitable aluminumsputtering target in a sputtering machine. These two half discs are thenseparately spin-coated with suitable liquid organic resins, bondedtogether with layer “zero” and layer “one” facing each other and theresin is cured with ultraviolet light. The distance within the discbetween the layer “zero” and the layer “one” is kept at about 55±5microns.

The reflectivity of the two information layers is measured from the sameside of the disc and found to be about the same 21 percent using a 650nanometers wavelength laser light. Electronic signals such as jitter andPI error are measured and found to be within published DVDspecifications. Subsequently, an accelerated aging test at 80 degrees C.and 85 percent relative humidity for 4 days is conducted on the disc.Afterwards, the reflectivity and the electronic signals are measuredagain and no significant changes are observed as compared to the samemeasurements made-before the aging test.

Example 5

A silver alloy sputtering target with the composition in atomic percentof about 0.2 percent lithium, 1.0 percent manganese, 0.3 percentgermanium and the balance silver is employed to produced thesemi-reflective layer of a DVD-9 dual layer disc. The procedure used tomake the discs is the same as the procedure used in the aforementionedexample 4. The reflectivity of the two information layers in thefinished disc is measured from the same side of the disc and found to beabout the same, about 22.5 percent using a 650 nanometers wavelengthlaser light. Electronic signals such as jitter and PI error are alsomeasured and found to be within published DVD specifications.Subsequently, an accelerated aging test at 70 degrees C. and 50 percentrelative humidity for 96 hours is conducted on the disc. Afterwards, thereflectivity and the electronic signals are measured again and nosignificant changes are observed compared to the same measurements madebefore the aging test.

It is understood that the same silver alloy thin film in this example,deposited on the disc with a thickness ranging from about 30 to about200 nanometers range can serve as the high reflectivity layer, such asLayer “one” in DVD-9 or Layer “two” in a tri-layer optical disc, asillustrated in FIG. 4. The same silver alloy can serve in other highreflectivity applications such as a rewritable optical disc such asDVD-RW, DVD-RAM in a general structure as illustrated in FIG. 5 at 650nanometers wavelength or any other future optical information storagemedium played back at around 400 nanometers wavelength.

Example 6

A silver based alloy sputtering target with a composition in a/o % ofapproximately 1.0% copper, 1.0% zinc, and the balance silver is used toproduce the reflective layer of another type of recordable disc a DVD−Rdisc or a DVD+R disc using the following procedure. Referring now toFIG. 2. An azo based recording dye is spin-coated on top of atransparent polycarbonate half disc about 0.6 mm thick and 12 cm indiameter with pregrooves suitable for DVD−R or DVD+R injection molded bya suitable stamper, and, dried. Subsequently, a reflective layer ofsilver based alloy approximately 150 nm in thickness is deposited orcoated on the recording dye using the sputtering target with theaforementioned composition in a magnetron sputtering machine.Afterwards, this half disc is bonded to another 0.6 mm thickness halfdisc using a UV cured resin. Information is recorded onto the disc in aDVD−R or DVD+R recorder and the quality of the electronic signal ismeasured.

The disc is then subjected to an accelerated aging test. The disc isheld at 80 degrees C. and 85% RH for 96 hours. Afterwards, thereflectivity and the electronic signals are measured again and nosignificant changes are observed as compared to the same measurementsbefore aging test.

Example 7

A process to make the sputtering target with the composition asindicated in example 6 is described hereafter. Suitable charges ofsilver, manganese and aluminum are put into the crucible of a suitablevacuum induction furnace. The vacuum furnace is pumped down to vacuumpressure of approximately 1 milli-torr and then induction heating isused to heat the charge. While the charge is heating up and theout-gassing finished, the furnace can be back filled with argon gas to apressure of about 0.2 to 0.4 atmosphere. Casting of the liquid melt canbe accomplished at a temperature approximately 10% above the meltingpoint of the charge. The graphite crucible holding the melt can beequipped with a graphite stopper at the bottom of the crucible.

Pouring of the molten metal into individual molds of each sputteringtarget can be accomplished by opening, and closing, the graphite stopperin synchrony with mechanically placing each mold into position justunderneath the melting crucible to that the proper amount of melt ispoured and cast into each mold. Afterwards, additional argon flow intothe vacuum furnace can be introduced to cool and quench the casting.Subsequently, a cold or warm multi-directional rolling process thatcauses a more than 50% reduction in thickness can be used to break upany nonuniform casting microstructure.

Then the final anneal is done at 550 to 600 degrees C. in a protectiveatmosphere for 15 to 30 minutes. After being machined into the rightshape and size, cleaned in detergent and properly dried, the finishedsputtering target is ready to be put into a magnetron sputteringapparatus to coat optical discs. Approximate sputtering parameterssufficient to make the semi-reflective layer of an ultra high densityoptical disc suitable for use with a playback laser with a wavelength of400 nanometers as mentioned in example 9 are as follows: 1 kilowatt ofsputtering power, 1 second of sputtering time, an argon partial pressureof 1 to 3 milli-torr, with a target to disc distance of approximately 4to 6 centimeters, giving a deposition rate of 10 nanometers per second.Using the same sputtering target and sputtering apparatus, the highreflectivity layer can be made with about the same sputtering parametersas the semi-reflective layer, except that to deposit the highreflectivity layer the sputtering power needs to be increased to 4 to 5kilowatts. Thus an ultra high density read-only optical disc, 5 inchesin diameter, with user storage capacity of about 20 to 25 giga bytes orhigher per side can be made in this manner. A dual layer disc with thestructure, illustrated in FIG. 3, has the capacity to storeapproximately 40 to 50 giga bytes of information, more than enoughstorage capacity for a full-length motion picture in the high-definitiondigital television format.

Example 8

The feasibility of using the same silver alloy thin film for both thereflective layer and the semi-reflective layer of a dual layer ultrahigh density read-only optical disc with a playback laser at awavelength of 400 nanomaters is investigated.

A silver alloy sputtering target with a composition given in a/o %: ofPd, 1.2%, Zn, 1.4% and balance silver was used to produce a dual layeroptical information storage medium as depicted in FIG. 3. A thin filmabout 10 nanometers thick of this silver alloy was deposited on asuitable polycarbonate substrate by using a magnetron sputteringmachine. Referring now to FIG. 3, the indices of refraction (n) of thetransparent substrate 214, the semi-reflective layer 216, the spacerlayer 218 and the high reflectivity layer are 1.605, 0.035, 1.52, 0.035,respectively. The extinction coefficient (k) for the semi-reflectivelayer and the high reflectivity layer is 2.0.

Calculations show that with a thickness of 24 nm, the semi-reflectivelayer will have a reflectivity R₀ of 0.242 and a transmission T₀ of0.600 in the disc at a wavelength of 400 nm. At a thickness of 55 nm,the high reflectivity layer will have a reflectivity R₁ of 0.685. Thereflectivity of the high reflectivity layer measured from outside thedisc through the semi-reflective layer will be R₀=R₁T₀ ² or 0.247. Inother words, to the detector outside the disc, the reflectivity fromboth the semi-reflective layer and the high reflectivity layer will beapproximately the same. This fulfills one important requirement for adual layered optical information storage medium, that the reflectivityfrom these 2 information layers be approximately equal, the relationshipbetween the optical properties of these two layers is R₀=R₁T₀ ².

Example 9

The same silver alloy used in example 8 can also be used as the highreflectivity layer and the two semi-reflective layers in a tri-layeroptical information storage medium for at playback using a laser with awavelength of 400 nm. Referring now to FIG. 4. Calculations show that,at a thickness of 16 nm for the first semi-reflective layer 316, athickness of 24 nm for the second semi-reflective layer 320, and athickness of 50 nm for the high reflectivity layer 324, thereflectivity, measured at the detector 332, will be 0.132, 0.137, 0.131,respectively. This shows that approximately the same reflectivity can beachieved from all three layers. Balance of reflectivity from all three,information layers can be achieved, using the same silver alloy.Additionally, one sputtering machine and one silver alloy sputteringtarget can be used to manufacture all three layers of an ultra highdensity tri-layer optical information storage medium suitable for usewith playback laser at wavelength 400 nm in a production environment. Itwill also be obvious, that aluminum alloys can also be used for the highreflectivity layer of this tri-layer medium

Example 10

A silver alloy sputtering target having the composition given in a/o %of: Pd, 0.4%; Cu, 1.5% and balance silver was used to produce the highreflectivity layer in a rewritable phase change disc structure such asDVD+RW, DVD−RW or DVD-RAM. Referring now to FIG. 5: Successive layers ofZnO.SiO₂, Ag—In—Sb—Te, and ZnO.SiO₂ of suitable thickness are coated ona 0.6 mm thick polycarbonate substrate which has continuous spiraltracks of grooves and lands made by injection molding from a suitablestamper. Next, a sputtering target with the aforementioned compositionis used in a magnetron sputtering apparatus to deposit a silver alloyfilm about 150 nm thick on top of the ZnO.SiO₂ film. Subsequently, thehalf disc is bonded with a suitable adhesive to the another 0.6 mm thickhalf disc of the same construction as the aforementioned half disc toform a complete disc.

Repeated record and erase cycles are performed in a suitable DVD+RW,DVD−RW or DVD-RAM drive. The disc meets the performance requirementsimposed on the recording medium. The disc further under goes anaccelerated environmental test at 80 degrees C., 85% relative humidityfor 4 days. Afterwards, disc performance is checked again, nosignificant change in the disc property is observed as compared to thedisc's performance before the environmental test.

Example 11

A silver alloy sputtering target having a composition given in a/o % of:Cu, 1.0%; Ag, 99.0% was used to produce the highly reflective layer in arewritable phase change disc structure or “DVR” as shown in FIG. 6. Inthis DVR structure, between dielectric layer 520 and highly reflectivelayer 522, there is an interface layer of SiC (not shown). The layers inthis example are deposited in the reverse order from the order of layeraddition used in Example 10. The transparent substrate 524 was made ofpolycarbonate and injection molded from a suitable stamper, then thesilver alloy reflective layer was deposited on the transparent substrateusing the above-mentioned sputtering target in a magnetron sputteringapparatus. Dielectric layer 520 (preferably ZnO.SiO₂), recording layer518 (preferably Ag—In—Sb—Te), another dielectric layer 516 (preferablyZnO.SiO₂) and an interface layer (preferably SiC) were then vacuumcoated, in sequence. Finally, the disc was covered with a layer of UVcured resin 514, 10 to 15 microns thick.

The performance of the disc was verified with a DVR type recording andplay back system using a 400 nm wavelength laser beam. Repeated recordand erase cycles were conducted satisfactorily. The disc is subjected toan accelerated environmental test. The disc is held at about 80 degreesC. and 85% relative humidity for 4 days. The performance of the disc wasagain checked and verified. No significant degradation of the disc'sproperty was observed.

While the invention has been illustrated and described in detail, thisis to be considered as illustrative and not restrictive of the patentrights. The reader should understand that only the preferred embodimentshave been presented and all changes and modifications that come withinthe spirit of the invention are included if the following claims or thelegal equivalent of these claims describes them.

1. An optical storage medium, comprising: a first layer having a patternof features in at least one major surface; a semi-reflective layeradjacent the pattern of features in said first layer, thesemi-reflective layer including a metal alloy, said metal alloyincluding silver, tin and indium, wherein the relationship between theamounts of silver, tin and indium in said metal alloy is defined byAg_(x)Sn_(y)In_(z), wherein 0.8<x<0.9998, 0.0001<y<0.10 and0.0001<z<0.10; a second layer having a pattern of features in at leastone major surface; and a reflective layer adjacent the pattern offeatures in said second layer.
 2. An optical storage medium, comprising:a first layer having a pattern of features in at least one majorsurface; a semi-reflective layer adjacent the pattern of features insaid first layer, the semi-reflective layer including a metal alloy,said metal alloy including silver and tin, wherein the relationshipbetween the amounts of silver and tin in said metal alloy is defined byAg_(x)Sn_(y), wherein 0.9<x<0.9999, and 0.0001<y<0.10; a second layerhaving a pattern of features in at least one major surface; and areflective layer adjacent the pattern of features in said second layer.3. An optical storage medium, comprising: a first layer having a patternof features in at least one major surface; a semi-reflective layeradjacent the pattern of features in said first layer, thesemi-reflective layer including a metal alloy, said metal alloyincluding silver and indium, wherein the relationship between theamounts of silver and indium in said metal alloy is defined byAg_(x)In_(z), wherein 0.9<x<0.9999, and 0.0001<z<0.10; a second layerhaving a pattern of features in at least one major surface; and areflective layer adjacent the pattern of features in said second layer.